The present invention relates to Radio Frequency (RF) Micro-electro-mechanical systems (MEMS) and devices that are fabricated on or within Low-Temperature Co-Fired Ceramic (xe2x80x9cLTCCxe2x80x9d) substrates. The present invention also relates to a method of fabricating, integrating and packaging such MEMS RF devices and systems using MEMS and LTCC technologies.
Microelectromechanical systems (MEMS) have been shown to be useful for a variety of consumer, industrial and military applications. Most MEMS devices are fabricated on semiconductor substrates (e.g., silicon, Gallium Arsenide, Silicon-On-Insulator, etc.) using standard Integrated Circuit (IC) processes in combination with specialized micromachining processes. Collectively these manufacturing technologies are frequently called microfabrication processes.
Conventional MEMS processes which are performed on silicon or other semiconductor substrates can lower the cost of products, but not to the extent required for many consumer or industrial applications. Typically, MEMS devices are batch fabricated, either as discrete components or directly on or within integrated circuits (xe2x80x9cICxe2x80x9d) as a part of a merged MEMS-IC process. Although both approaches can potentially lower cost somewhat, the reduction is not sufficient for many applications. Even if a sufficiently low cost process for the fabrication a MEMS device can be achieved, the manufacturing of MEMS devices can incur significant additional costs associated with packaging and integration, resulting in an expensive overall system or product cost. The fabrication of MEMS devices directly on or within integrated circuits (xe2x80x9cintegrated MEMSxe2x80x9d) requires expensive process development as well as some compromises in device performance. Both approaches are also limited by total processing area, and the resultant gains from these approaches are modest at best. Consequently, one of the key limitations of MEMS technology has been the cost of manufacturing MEMS devices and systems using semiconductor substrates and microfabrication process technologies. Another limitation relates to the high cost associated with packaging these devices and systems. Yet another limitation relates to the cost and difficulty of realizing systems wherein MEMS and microelectronics are combined into modules or integrated together to form functional systems. Therefore, there is a tremendous need for more functional and cost-effective fabrication, packaging and integration techniques for implementation of MEMS-based RF devices.
Recently there has been a large interest in making MEMS Radio Frequency (RF) devices and systems for a variety of high volume communication applications. Although MEMS-based RF components and systems have been demonstrated, all have been realized on traditional semiconductor materials, primarily silicon wafers. While this approach works for the demonstration of a device, it has several severe disadvantages for the performance and potential commercialization of RF and microwave devices. First, the dielectric losses of the silicon substrate are very high at frequencies above 1 GHz. Second, the cost of silicon substrates and processes used to fabricate MEMS RF devices on these substrates are too high compared to existing technologies. Third, the packaging costs of silicon and other semiconductor material based MEMS devices are very high, particularly for devices that must operate at high frequencies and under extreme environmental conditions.
While the losses of the silicon substrate can be reduced appreciably by selectively removing the silicon from under the active devices and the associated signal paths using an isotropic etchant, such as Xenon Diflouride (XeF2), this is an expensive process and one that is not readily compatible with the fabrication of active MEMS devices. Consequently, the resultant manufacturing yield will be low and the cost will increase appreciably. Other semiconductor substrates having lower dielectric losses can be employed for the fabrication of MEMS devices, such as Gallium Arsenide (GaAs), resulting in high performance devices. However, the cost of these materials and the costs to fabricate devices on these materials are typically two orders of magnitude higher than even silicon wafers and processes. Consequently, the resultant device or system cost will be far too high for many consumer or industrial applications. Furthermore, any semiconductor based MEMS device will require a separate packaging technology that will need to be specifically developed to meet the demanding requirements of a commercial product. Packaging techniques that can meet the required specifications and simultaneously provide a sufficiently low cost have not been readily available in the past.
Nevertheless, there is enormous opportunity for MEMS technology in the application of RF and microwave devices and systems. If the cost and performance goals can be met, the potential market sizes for these devices will be enormous. However, in order to exploit this opportunity, there is a need for a new low-cost material that has low dielectric losses at high frequencies and onto which MEMS devices can be successfully fabricated with high yield. Furthermore, there is a need for the capability to suitably and inexpensively integrate these MEMS devices with other MEMS device and components to form functional systems. There is also a need to suitably and inexpensively package MEMS devices and systems. It is useful to elaborate in some detail about specific RF and microwave MEMS devices and systems that can greatly benefit from fabrication, packaging and integration that can be performed on a low-cost low dielectric loss material.
MEMS Radio Frequency (RF) switches have been shown to have very low dielectric losses at very high frequencies, if fabricated on specialized substrate materials such as GaAs. Compared to traditional active microwave switches (based on active components such as transistors or diodes), the quality factors (where the quality factor is given by 1/Ron Coff, where Ron is the resistance of the switch in the ON-state and Coff is the OFF-state capacitance of the switch) of these MEMS RF switches are very high. Therefore, MEMS RF switch components have the potential for use in many types of applications. However, these devices have been limited due to the extremely high cost of fabricating and packaging the MEMS switches on Gallium-Arsenide substrates.
An important application of MEMS switches is as phase-shifters in phased-array antennas. Traditionally, phase-shifters for phased-array antennas have been implemented using active electronic components (e.g., transistors, diodes, etc.) made from exotic and expensive materials such as Gallium-Arsenide (GaAs). Typically, even at high volume production, GaAs-based active phase-shifters can cost more than 100 times to fabricate and are more than twice as lossy as MEMS phase-shifters. As a result, phase-shifters are the main cost driver in phased-array antennas. If active electronic GaAs phase-shifters are employed, about 45% of the overall cost of a receiver antenna system can be attributed to the phase-shifters alone. This is attributed to the high fabrication cost for such devices and the additional cost associated with the amplification and thermal management required by their high losses at their operational frequencies. Consequently, due to the high cost, active electronic GaAs-based phase-shifters have been limited to use in military array antennas.
For similar reasons, a variety of other-MEMS RF components and systems, including: electronically-tunable variable capacitors, closed-loop controlled variable capacitors, tunable inductors, tunable LC filters, tunable LC networks, reconfigurable RF antennas, phased array antennas, as well as combinations of the above MEMS devices and systems, would greatly benefit from the ability to be fabricated on a low-cost, low dielectric loss material. Furthermore, these devices and systems would also benefit from low-cost and high performance approach for packaging and integration.
Recent developments in Low Temperature Co-Fired Ceramic (LTCC) processing, combined with the recent availability of new high-quality LTCC substrate materials having low dielectric losses at high frequencies, have made it possible to fabricate, integrate and package RF MEMS devices and systems with high performance and at low costs.
Direct fabrication of MEMS RF components onto LTCC substrates is key to reducing the cost of these systems, while simultaneously achieving high functional performance. The use of LTCC substrates and processing techniques to integrate and/or package MEMS RF devices also provides many advantages. The cost to attempt to integrate different types of MEMS RF devices together or with microelectronics is enormous. This is because the processing steps used to fabricated the merged devices or systems greatly influence material properties and resultant device performance. Using LTCC as a substrate material greatly simplifies and lowers the cost of integration.
With respect to packaging, it is frequently the case that the cost of packaging MEMS devices is more than the cost of the MEMS device itself. This is because the package must be specifically designed and manufactured for each individual MEMS device type. Furthermore, the package must protect the MEMS device from the environment, but simultaneously allow the MEMS device to interact with the environment. The use of LTCC as a substrate material that can provide electrical connections through layers, as well as methods to make MEMS directly on the LTCC material, and methods to affixed semiconductor substrates with high quality electrical connections to the activated components, while also providing suitable packaging protection, and at low cost, is a significant improvement in MEMS technology.
The present invention, which uses MEMS RF devices fabricated on a LTCC substrate, allows the cost and difficulty of realizing a system to be dramatically reduced so that MEMS RF devices can be more broadly used for consumer and industrial applications. The present invention, which uses an LTCC substrate with electrical connections across or through multiple layers of the LTCC substrate, and when bonded or affixed to MEMS on LTCC substrates or other substrates such as semiconductor ICs, enables the device or system to be integrated and packaged with a significant reduction in cost so that products based on MEMS technology can be used more broadly for consumer and industrial applications.
The present invention, which uses MEMS RF switches fabricated on an LTCC substrate, allows the cost of MEMS RF switches to be dramatically reduced while maintaining excellent RF performance, so that they can be used more broadly for mobile wireless communication systems, including broadband satellite communications and broadband cellular communications, and thereby be available for use by a wide consumer base.
The present invention, which uses any single or combination of MEMS components, including: electronically-tunable variable capacitors, closed-loop controlled variable capacitors, tunable inductors, tunable LC filters, tunable LC networks, fabricated on an LTCC substrate, allows the cost of MEMS devices to be dramatically reduced while simultaneously achieving high performance and functionality so that these devices and systems can be more broadly used for mobile wireless communication systems, broadband satellite communications or broadband cellular communications, and thereby be available for use by a wide consumer base.
The present invention, which uses MEMS RF switches and/or phase shifters fabricated on an LTCC substrate, allows the cost of phased-array antennas to be dramatically reduced so that phased-array antennas can be more broadly used for mobile wireless communication systems, including broadband satellite communications and broadband cellular communications, and thereby be available for use by a wide consumer base.
Furthermore, the present invention also enables the fabrication and packaging of other micromechanical and microelectronic components, either discrete or integrated, onto substrate materials which have high-performance characteristics at elevated operational frequencies and low-cost.
An object of the present invention is to provide integrated MEMS RF devices, RF switches, and phase shifters fabricated on and/or packaged within low-cost Low-Temperature Co-Fired Ceramic (LTCC) substrates.
Another object of the present invention is to provide integrated and packaged MEMS tunable inductors; electronically tunable variable inductors; closed-loop controlled electronically tunable variable inductors; RF switches; electronically-controllable phase-shifters, variable capacitors; electronically tunable variable capacitors; closed-loop controlled electronically tunable variable capacitors; fabricated on and/or packaged with low-cost LTCC substrates.
A further object of the present invention is to provide an integrated, low-cost and highly functional, high-performance, high-gain phased-array antenna using MEMS phase-shifters and other microfabricated electrical and microwave components combined with LTCC substrates.
Another object of the present invention is to provide a method for fabricating phased-array antenna modules that can be subsequently tiled together with a number of indentical antenna modules to form an entire phased-array antenna system.
Another object of the present invention is to provide an entire integrated, highly-functional, high-gain phased-array antenna system composed of micromechanical, microelectronic and microwave components on a large low-cost and low-dielectric loss LTCC substrate material.
Yet another object of the present invention is to provide a process for manufacturing high-performance and high quality MEMS devices and other electronic and microwave components on LTCC substrate materials.
Another object of the present invention is to provide a process for manufacturing high-performance and high quality MEMS devices and other electronic and microwave components onto multiply layered LTCC substrate materials enabling efficient electrical connection between the conduction lines and components on individual layers.
Another object of the present invention is to reduce the manufacturing cost of high-gain phased-array antennas.
A further object of the present invention is to provide a method of efficiently integrating and packaging MEMS devices and other functional components, such as microelectronic and microwave devices including: MEMS tunable inductors; electronically tunable variable inductors; closed-loop controlled electronically tunable variable inductors; electronically-controllable phase-shifters; RF switches; variable capacitors; electronically tunable variable capacitors; closed-loop controlled electronically tunable variable capacitors; within suitably patterned and adjoined multiply-layered LTCC substrates.
A further object of the present invention is to provide a method of efficiently packaging MEMS device in LTCC modules on which other integrated circuits can be mounted to form the phased-array antenna of the present invention.
Yet another object of the present invention is to provide a very low cost and effective means of batch fabricating individual discrete or integrated MEMS, microelectronic, and microwave components such as MEMS tunable inductors; electronically tunable variable inductors; closed-loop controlled electronically tunable variable inductors; electronically-controllable phase-shifters, RF switches, variable capacitors; electronically tunable variable capacitors; closed-loop controlled electronically tunable variable capacitors; on LTCC substrate materials as well as providing a packages for these components from suitably patterned and adjoined multiply-layered LTCC substrates.
Yet another object of the present invention is to provide very cost effective packaging of MEMS devices in LTCC modules for applications other than array antennas.
The present invention is directed to the embodiment of MEMS devices onto or within LTCC substrates and the embodiment of discrete MEMS RF, electronic, and microwave components onto LTCC substrates.
The present invention is also directed to an integrated, low-cost and highly functional, high-gain MEMS-based phased-array antenna that can be tiled together with a number of antenna modules to form an entire phased-array antenna system and that can be made from suitably adjoining a multiplicity of large LTCC substrate materials. The present invention is also directed to an improved method of manufacturing the MEMS-based LTCC antenna and other devices that use MEMS and LTCC technology and to the packaging of discrete MEMS, electronic, and microwave components within suitably patterned and adjoined multiply layered LTCC substrates.
The device or system of the present invention is a multi-layered structure, which contains a number of passive and active elements, some of which are MEMS devices, which are preferably fabricated onto suitably patterned and adjoined multiple layered stack of LTCC substrates.
In yet another embodiment of the present invention, discrete MEMS, microelectronic and microwave components, such as MEMS tunable inductors; electronically tunable variable inductors; closed-loop controlled electronically tunable variable inductors; electronically-controllable phase-shifters; RF switches; variable capacitors; electronically tunable variable capacitors; closed-loop controlled electronically tunable variable capacitors; and other components commonly used in the implementation of high frequency devices and systems, are batch fabricated and packaged onto and within a suitably patterned and adjoined multiple layered stack of LTCC substrates. The discrete components can be separated from the substrates using any of the well known and established methods of die separation such as diesawing.
In yet another embodiment of the present invention a phased-array antenna is a multi-layered structure, which contains a sub-array of wide-band radiating patches, a corresponding number of digital phase shifters, a power divider (or combiner) network, and a band pass filter at the input (or output) of the antenna. The antenna layers preferably use LTCC material as a dielectric substrate and the various circuit components formed by the different layers are integrated together via vertical interconnects. This level of integration and the use of LTCC material results in a rugged and power efficient antenna, which allows a significant reduction in the cost of phased-array antenna systems, while improving the overall performance of such systems. The modularity of one embodiment of the design greatly simplifies the integration of the large phased-array that can be assembled using the antenna modules of the present invention as its building blocks. Similar designs are employed for the transmitting and receiving antennas.
Alternatively, the entire antenna system can also be implemented using a multiplicity of suitably patterned and adjoined large sheets of LTCC material unto which the various components are fabricated to embody a complete and functional phased-array antenna system. In yet another embodiment of the present invention, micromechanical and microelectronic components, either discrete or integrated onto substrate materials which have high-performance characteristics at elevated operational frequencies, are fabricated, integrated and packaged on LTCC substrates.
According to the method of the present invention, the use of large LTCC wafers or panels, without compromising processing capability or speed, lowers the cost of fabrication dramatically. Panels as large as 1xc3x971 m can be manufactured in LTCC lines, as compared to 0.3 m diameter wafers used in state-of-the-art semiconductor IC foundries. Moreover, the tools and fabrication methods needed to process large LTCC panels are not as expensive as those needed to process semiconductor wafers, since the minimum size of patterned features, such as conducting strips and via holes, is more than 25 xcexcm. The savings on the tool costs and the fabrication of significantly more devices for the equivalent effort and cost yields very low-cost fabrication.
Alternatively, LTCC substrates can be embodied in the form of wafer sizes and dimensions standard to the semiconductor processing industry and equipment set, thereby allowing the fabrication of high-performance devices and systems on the existing semiconductor processing equipment base.
The method of the present invention also does not require separate packaging and integration steps for the MEMS components. In the present invention, a multiplicity of suitably patterned LTCC material layers are stacked or adjoined together and used as substrates onto which are fabricated high-performance MEMS components that are required to build high frequency devices and systems including: MEMS tunable inductors; electronically tunable variable inductors; closed-loop controlled electronically tunable variable inductors; electronically-controllable phase-shifters; RF switches; variable capacitors; electronically tunable variable capacitors; closed-loop controlled electronically tunable variable capacitors; and other components commonly used in the implementation of high frequency devices and systems.
Alternatively, a variety of MEMS devices and other components, some of which are fabricated directly onto the LTCC systems, others of which are made on other substrates such as microelectronics die, can be integrated with the LTCC layers to build a phased-array antenna, or other high frequency devices and systems.
These components that can be fabricated on the LTCC substrates for the embodiment of RF systems or phased-array antennas including, for example, transmission lines, couplers, dividers, filters and radiating patches.
Providing the vertical connections between layers necessary for an array antenna, a discrete MEMS component, or an array of MEMS components, is straightforward and efficient in an LTCC process, whether on a panel, sheet or wafer shaped substrate, in comparison to standard semiconductor processes using conventional substrate materials, and where such connections are extremely difficult and expensive.
According to the method of the present invention, two or more multilayer ceramic modules or substrates are formed using a standard LTCC process are combined with microfabrication processes as part of the present invention. After appropriate surface preparation on one of the modules or substrates, MEMS devices are formed on the frontside of that module or substrate. Next, the two ceramic modules or substrates are bonded or adjoined together, forming a hermetically sealed cavity in which the MEMS devices are located. The bonding is preferably performed in a controlled environment to modify and improve the operation of the MEMS devices. Finally, various types of ICs can be flip-chip bonded or wire bonded to the backside of the module on which the MEMS devices are fabricated. These ICs can also be packaged by bonding or adjoining two or more modules or substrates to form a sealed cavity. At this step, if necessary, thermal spreaders are then mounted on the ICs. It should be obvious to those skilled in the are that this method can be extended as a low-cost and efficient method to package a variety of other high frequency micromechanical, electronic and microwave components and systems. Efficient electrical connections between components and systems located on different layers of the stack of multiple layers are enabled with this method.
From the point of view of MEMS fabrication, for an embodiment of a phased array antenna, one or more ceramic modules are the substrates on which the MEMS devices are fabricated, and the other modules are the top cover of a hermetically sealed cavity containing the MEMS devices. From the point of view of the phased-array antenna, the layer of MEMS devices is only one of many device layers that make up the overall architecture of the antenna. The layer with the MEMS devices (and corresponding transmission lines) is referred as the phase-shifter layer. The other ceramic layers that form the ceramic modules are used to form circuits, such as power dividers or combiners, filters, couplers, polarizers, etc. Finally, for semiconductor Ics, the ceramic modules can also serve as the integration and packaging medium.
The phased array antenna and phase-shifter combination of the present invention results in a design in which there are many antenna radiating elements with slight phase-shifts with respect to each other, thereby allowing the use of an electronically scanable beam without mechanically changing the position of the phased array antenna.
The present invention also results in an extremely low-cost method for batch fabricating and packaging discrete MEMS, electronic and microwave components. The present invention also results in an extremely low-cost method for batch fabricating and packaging discrete MEMS RF switches and integrated MEMS phase-shifters.
The present invention also results in an extremely low-cost method for batch fabricating and packaging integrated MEMS tunable inductors; electronically tunable variable inductors; closed-loop controlled electronically tunable variable inductors; RF switches; electronically-controllable phase-shifters, variable capacitors; electronically tunable variable capacitors; and closed-loop controlled electronically tunable variable capacitors, as well as combinations of the above devices.
The present invention also results in an extremely low-cost method for batch fabricating and packaging integrated phased-array antennas, and, in particular, integrated phased-array antennas that can be subsequently tiled together with a number of identical antenna modules to form an entire phased-array antenna system.
The present invention also results in an extremely low-cost method for batch fabricating and packaging high quality MEMS devices and other electronic and microwave components on LTCC substrate materials.
The present invention is directed to the embodiment of MEMS devices and systems, in particular RF MEMS devices and systems onto or within LTCC substrates. The present invention is also directed to the embodiment of discrete MEMS, electronic, and microwave components onto LTCC substrates.